A thin-wall metal tube having a predetermined length is manufactured by a process including: rounding a thin metal sheet having a larger length than the predetermined length in such manner that two parallel edges thereof are brought close to each other; welding the two edges together to form a cylindrical tube; and cutting the tube to the predetermined length. One known cutting apparatus for use in cutting such a tube is configured to move a cutting tool abutting against the outer peripheral surface of the tube toward the inside of the tube radially of the tube (see patent document 1 for example).
In cutting a thin-wall tube having a low strength with such an apparatus configured to move a cutting tool from the outer peripheral surface toward the inside of the tube, however, the thin-wall tube is deformed radially, thus lowering the roundness of the resulting product.
In view of this inconvenience, a tube cutting apparatus for use in cutting such a thin-wall tube has heretofore been proposed which is configured to position an outer blade so as to contact an outer peripheral surface of the tube and move an inner blade positioned inside the thin-wall tube toward the outside of the tube while rotating the inner blade.
In this case, use of a hollow shaft member and an inclined cam can be conceived for applying the inner blade with a moving force acting radially of the tube while transmitting rotation to the inner blade. The hollow shaft member is adapted to be inserted into the tube coaxially with the tube, supports thereon the inner blade by a retainer member at a predetermined axial position for rotation and radial movement, and accommodates therein the inclined cam abutting against the retainer member for axial movement.
As the inclined cam moves axially of the hollow shaft member with the hollow shaft member rotating, the position of contact between the retainer member and the inclined cam is displaced radially of the tube to cause the inner blade to move radially of the tube and rotate.
Patent Document: Japanese Patent Laid-Open Publication No. H7-136981